// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_THREADING_WORKER_POOL_H_
#define BASE_THREADING_WORKER_POOL_H_

#include "base/base_export.h"
#include "base/callback_forward.h"
#include "base/memory/ref_counted.h"

class Task;

namespace tracked_objects {
class Location;
} // namespace tracked_objects

namespace base {

class TaskRunner;

// This is a facility that runs tasks that don't require a specific thread or
// a message loop.
//
// WARNING: This shouldn't be used unless absolutely necessary. We don't wait
// for the worker pool threads to finish on shutdown, so the tasks running
// inside the pool must be extremely careful about other objects they access
// (MessageLoops, Singletons, etc). During shutdown these object may no longer
// exist.
class BASE_EXPORT WorkerPool {
public:
    // This function posts |task| to run on a worker thread.  |task_is_slow|
    // should be used for tasks that will take a long time to execute.  Returns
    // false if |task| could not be posted to a worker thread.  Regardless of
    // return value, ownership of |task| is transferred to the worker pool.
    static bool PostTask(const tracked_objects::Location& from_here,
        const base::Closure& task, bool task_is_slow);

    // Just like TaskRunner::PostTaskAndReply, except the destination
    // for |task| is a worker thread and you can specify |task_is_slow| just
    // like you can for PostTask above.
    static bool PostTaskAndReply(const tracked_objects::Location& from_here,
        const Closure& task,
        const Closure& reply,
        bool task_is_slow);

    // Return true if the current thread is one that this WorkerPool runs tasks
    // on.  (Note that if the Windows worker pool is used without going through
    // this WorkerPool interface, RunsTasksOnCurrentThread would return false on
    // those threads.)
    static bool RunsTasksOnCurrentThread();

    // Get a TaskRunner wrapper which posts to the WorkerPool using the given
    // |task_is_slow| behavior.
    static const scoped_refptr<TaskRunner>& GetTaskRunner(bool task_is_slow);
};

} // namespace base

#endif // BASE_THREADING_WORKER_POOL_H_
